The present invention relates to a resist material used in the manufacture of semiconductor devices and a polymer composition used for such a resist material. More particularly the invention pertains to a resist material used for forming a positive pattern by applying ultraviolet light, especially deep ultraviolet light with a wavelength not greater than 300 nm, KrF eximer laser beams or the like as exposure energy source, and a polymer composition used for such a resist material.
With a recent trend toward higher-density integration of semiconductor devices, necessity has been intensified for shortening of the wavelength of the energy source of exposure means used for fine working, particularly in the art of photolithography, and now use of deep ultraviolet light (300 nm or less in wavelength), KrF excimer laser beams (248.4 nm) and the like is seriously considered. However, there not has yet been available a resist material applicable to practical use with such short-wavelength exposure light.
As a resist material usable for pattern formation with KrF excimer laser beams or deep ultraviolet light as light source, there have been known the dissolution-inhibiting type resist materials composed of a polymer having high transmittance of light near 248.4 nm and a photosensitive compound having a diazodiketo group (JP-A 1-80944; JP-A 1-154048; JP-A 1-155338; JP-A 1-155339; JP-A 1-188852; Y.Tani et al: Proc. SPIE, 1086, 22 (1989), etc.). These dissolution-inhibiting type resist materials, however, are low in sensitivity and unapplicable to use with deep ultraviolet light or KrF excimer laser beams wherein use of a high-sensitivity resist material is required. Also, as means for reducing the energy required for exposure (high-sensitization), the chemically amplified type resist materials making use of an acid generated on exposure as medium have been proposed (Ito et al: Polym. Eng. Sci., 23, 1012 (1983)), and many reports have been published on this type of resist materials (U.S. Pat. No. 4,491,628 (1985) to H. Ito el al (=JP-A 2-27660); U.S. Pat. No. 4,603,101 (1986) to J. C. Crivello et al (=JP-A 62-115440) W. R. Brunsvolt et al: Proc. SPIE, 1086, 357 (1989); T. X. Neenan et al: Proc. SPIE, 1086, 2 (1989); R. G. Tarascon et al: SPE Regional Conference Technical Papers, Ellenville, N.Y., 1988, p. 11; JP-A 2-25850; Y. Jian et al: Polym. Mater. Sci. & Eng., 66, 41 (1992), etc.). These conventional chemically amplified type resist materials, however, had disadvantages in that they were liable to cause peeling of the film during development due to poor adhesion to the substrate especially when the polymer used for the resist material is a phenol ether type polymer such as poly(p-tert-butoxycarbonyloxystyrene), poly(p-tert-butoxystyrene), poly(p-tert-butoxy-carbonyloxy-.alpha.-methylstyrene), poly(p-tert-butoxy-.alpha.-methylstyrene), poly(p-tert-butylisopropenylphenoxyacetate), poly(p-tert-butoxycarbonyloxystyrene/sulfone), poly(p-tetrahydropyranyloxystyrene), poly{p-(1-methoxyethoxy)styrene}, poly{p-(1-phenoxyethoxy)styrene} or the like. They were also poor in heat resistance, and thus were unable to form a good pattern. Other problems of these resist materials included poor resolution due to poor light transmittance near 248.4 nm owing to the presence of benzoyl groups in the case of carboxylic acid-ester type polymers such as poly(p-tert-butylvinylbenzoate) and poly(p-tetrahydropyranylvinylbenzoate) and poor heat resistance and poor dry etch resistance in the case of polymers such as poly(tert-butyl methacrylate).
The resist materials comprising silicon-containing polymers have also been disclosed (JP-B-3-44290, etc.), but they involve difficulties in realizing their practical use because of problems such as low sensitivity and incapability of perfect removal by ashing due to inclusion of silicon in case of using, for instance, poly(p-trimethylsilyloxystyrene) or poly(p-tert-butyldimethylsilyloxystyrene).
Lately, as the chemically amplified type resist materials improved in these defects, there have been disclosed the resist materials using poly(p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene) (JP-A 2-209977 and JP-A 3-206458), the resist materials using poly(p-tetrahydropyranyloxystyrene/p-hydroxystyrene) (JP-A 2-19847, JP-A 2-161436 and JP-A 3-83063), and the resist materials using poly(p-tert-butoxystyrene/p-hydroxystyrene) [JP-A 2-62544 and JP-A 4-211258 (U.S. Pat. No. 5,350,660)]. The resist materials comprising these polymers, however, are incapable of offering a high resolution which is strongly required in this art in recent years, and also have their own problems in delay time (a problem of variation of pattern size with the lapse of time during the period from application of the resist to exposure to light, or from exposure to light to heat treatment (PEB), deterioration of pattern shape) which comes into question in practical use and a problem of substrate dependency (the problem that the pattern is formed or not formed depending on the kind of the material used as semiconductor substrate such as SiO.sub.2, Si.sub.3 N.sub.4, Ti.sub.3 N.sub.4, BPSG, polysilicon or the like).
Resist materials comprising a polymer (such as poly(p-1-methoxyethoxystyrene/p-hydroxystyrene) into which an acetal group or a ketal group has been introduced as protective group) and a photoacid generator such as a triphenylsulfonium salt derivative or a diphenyliodonium salt (JP-A 2-161436, JP-A 4-219757, JP-A 5-281745, JP-A 3-282550, etc.) have also been disclosed. These resist materials, however, involve the problem of scum (a problem caused by generated scum which may be transferred to the substrate during etching) and/or the problems of substrate dependency and delay time. JP-A 5-249682 discloses a resist material comprising a combination of a polymer such as poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene), poly(p-1-methoxy-1-methylethoxystyrene/p-hydroxystyrene), poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/methyl methacrylate) or poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/fumaronitrile) and a photoacid generator such as a diazodisulfone compound. These materials have many excellent qualities such as high resolution and minimized delay time, but they still have the problems of substrate dependency and generation of scums. JP-A 6-194842 discloses a resist material comprising a combination of a polymer such as poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/p-tert-butoxystyrene) and a photoacid generator such as a diazodisulfone compound. This material, although excellent in such matters as resolution, mask linearity, heat resistance and delay time, is not free of the problems of substrate dependency and scum. EP-A 679,951 reports a resist material characterized by mixed use of two different polymers: poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene) and poly(p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene). This resist material, however, still involves the problems relating to the resolution and the delay time.
As described above, the chemically amplified type resist materials are remarkably improved in sensitivity as compared with the conventional resist materials, but they still involve the problems such as poor heat resistance of the polymer used therefor, insufficient adhesiveness to the substrate, unsatisfactory transmittance of light with a wavelength of around 248.4 nm, unsatisfactory resolution, pattern size variation or deterioration of pattern shape with the lapse of time, low storage stability, insufficient focus margin, poor mask linearity, footing (broader bottom shape of the pattern), generation of scum and high substrate dependency, resulting in preventing these materials from practical use. Thus, the development of a practical high-sensitivity resist material free of the problems mentioned above has been keenly desired.